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Magazine

Interview

Winter 2004

Professor of Physics Dale SyphersWhen he's not teaching classes, playing noontime basketball, or otherwise engaged on campus, Dale Syphers can often be found in the business of providing expert testimony in the area of accident reconstruction. We talked to Dale about his sideline business of using physics in the real world.

SH: Tell us about your accident reconstruction work.

DS: It's basically applied physics Ñ physics in the real world, where most of us live, not in the journal world, where I do my research. I got into this because years ago there was a Physics Today article, and the writer was talking about the need for physicists to have a greater presence in society as a whole and especially in things like the courtroom. His example was a trial in New Jersey, where a lawyer summed up by saying after hearing expert testimony, "Well, we all know the laws of physics are made in the laboratory, but, ladies and gentlemen of the jury, we know it's a different thing entirely on the roads of New Jersey." And that lawyer won.

SH: So that will get your blood boiling! You need to get in there and show that the physics actually do apply to the Garden State Parkway!

DS: Exactly. But it's fascinating. What I've learned is, much like the stuff I do in my research, I can't see, I can't tell what's going on, other than by what the data tells me. And it's all removed Ð I never get to actually watch my electrons doing anything. Same thing here. I come, and I find evidence. I look around and I just keep asking the same kind of questions Ð what is it trying to tell me? What's the information, where is it hidden? And that's led to some very interesting cases.

SH: Is this all auto-related accidents? What kind of accidents are we talking about?

DS: Most of it is auto, but it extends from everything from electrostatic shocks that people receive on warming trays at McDonald's toÉ

SH: Somebody gets shocked on a warming tray at McDonaldÕs and they file a lawsuit?

DS: Yes. Their electricians looked it over, and they said there didn't appear to be anything wrong with the unit, and so they called me and said "do you have any expertise you could use that would apply to this?" So I looked at the unit, I asked what the guy was wearing, where the McDonald's was, what time of year and so forth, and I looked up the temperature charts. It was the coldest day of the year, and he was wearing a polypropolene jacket, he slid on a naugahyde bench and went to this warming tray just loaded with static electricity.

SH: All right, so presumably, there's an accident, the police come, check and make sure everybody's OK, clear the stuff out of thereÉ.what's left? Cause you don't go there the day of the accident.

This is a typical accident scene as Professor Syphers first sees it. "The challenge is to determine which marks on the road are associated with the accident and how they occurred," he explains. "This scene shows some straight skid marks which occurred right before the 'point of impact' ('POI' on the road), some gouges in the roadway where the crushed front ends of both cars dragged through the pavement, showing their initial trajectories, and some spray paint marks showing where the vehicles ended up."

DS: Occasionally I do, and occasionally I happen upon accidents, and after being in this a little while, I've learned whenever I'm going by an accident, if I'm not late for something, I actually stop and take a look, because you wouldn't believe the number of times where I get a call for something, and I say "I was there. I witnessed it." Or I was there right afterwards. So now I actually stop.

SH: But if you are sent to a scene, other than maybe tire tracks, what are you looking at?

This is a picture of the same car as above. "The deformation of the car is being measured to get a sense of the magnitude of the impact," explains Syphers. "I can also use this deformation to get an estimate of the relative speeds of the two vehicles."

DS: Well, there are tire tracks, there are gouges in the road, there are debris fields. Debris fields are interesting.

SH: You're basically there pretty soon after the accident, then.

DS: Sometimes. Sometimes it's a ways after É

SH: And haven't they cleaned all that stuff up?

DS: Yeah. Well, they don't clean it up. What they do is sweep it to the side, so it's still there, but it's on the side. And you try to find the person who did the cleaning and say "did you sweep it down the roadway, or did you just sweep it to the side of the road?" Nine times out of ten the answer is "swept it to the side of the road." They don't sweep it twenty feet down the street and then over. So, therefore, what's on the side of the road is usually a pretty good indicator of where it was.

SH: So you look at debris, you look at tire marksÉ

DS: And you look at the vehicles themselves. You go and look at them and photograph them, stuff like that. That tells you a lot about the angle of impact. There was a criminal case, where somebody was in a collision at 2 a.m., (surprise, surprise, when the bars close).

Looking at the spacing of the black lines left on the vehicle's body, and comparing with the tire that made them, Syphers could determine the relative speed of the two vehicles, how they were oriented at the time of collision, and (with other information from the scene) who was responsible for initiating contact.

And the evidence that I used was a tire mark from one car onto the fender of the other car, and from the mark that it left, I was able to look at the tire and figure out a certain pattern Ð this was one of those ones where I looked at it and I said, "thereÕs information here, I just gotta figure out how to get it out." And it turned out that there was a sequence of places where there wasn't rubber on the fender and that turned out to be the places with the little tiny eighth-inch long nub from the injection molding machine that stick out from the tire were folded over and slid along. And those occurred at certain distances Ð there were about 12 of them or 10 of them around the tire Ð and that allowed me to figure out what the relative speed between the cars was. And contradict what the other, the police accident specialist, said. And the case was dropped, and the person was set free.

AB: So, are you always able to in these cases make science overrule police experience or judgment or witness testimony?

DS: When I'm finished with a reconstruction, I'm pretty sure about what happened. I'm more than pretty sure Ð actually I find that in most cases there's too much information. That is, I don't just get one answer Ð there's about four different paths that use information that all have to correlate. So it creates sort of a fabric and by the time I'm done, and everything comes into the same answer, I know that's the answer Ð that's what happened. (But) how is that used, and does it overrule? And the answer is, it depends. Sometimes it does, sometimes it depends on what the jury and the judge and anyone else involved thinks is more important. For instance, in several cases it's been clear and I'm able to show that someone is speeding 15 miles an hour over the limitÉ

SH: How do you do that?

DS: By looking at the conservation of angular momentum and conservation of linear momentum and conservation of energy and apply the dynamic physical formulas that we teach students here to the specific situations. There are other little tricks Ð for instance, there are material tricks that you learn when you're in the business a while.

"It may be hard to see, but if you look closely at these brake light bulbs you'll notice that the filament is not in a straight horizontal line, but instead is bowed out in an arc," Syphers points out. "This tells me that the brake lights were on at the time of the collision. When the bulbs were installed, the filament was horizontal between the posts, but when it is glowing it is easily deformed into a new shape if it is accelerated while hot. The acceleration due to the collision resulted in the 'bowed out' filament, proving that the driver had their brakes on at the time of the crash."

Like we can tell if you had your blinker on, when you're in an accident, or your brakes, or whatever. Because the filament glows, and because it glows, it gets very hot, and if you have an accident with a high accelearation, it gets very plastic, it's not metallic anywmore, and so it warps. So you know things like that.

SH: You're not writing reports and handing them off. You're actually going into the courtroom to testify.

DS: Yeah, I give depositions. And I go to court. I hate my coutroom time actually, it's highly stressful.

SH: You're an advocate for the science, but also for your employer, the insurance company.

DS: Yes. Everyone has to make their own peace with how that functions, and I've made mine the way that I will say whatever I can say that is definitely true for the person who's employing me. I won't lie. If someone asks me a question that totally undermines their case and it's correct, I will answer that, and I tell everybody that. And half the times I get called by lawyers, my initial answer after looking at the site is "I canÕt help you. There's nothing I can say that will help you."

SH: Do you ever use any of this experience in the classroom?

DS: Yes. I worked a little bit with Bill Barker to construct a motorcycle accident scenario for use in their calculus program, and I use it in courses that I teach here. Often the lessons one leaves physics with are somewhat esoteric lessons, but I also try to leave students with life lessons, like how to recognize when you're about to have a collision. We have a problem we assign that has them figure out what's happening in relative motion between two objects, and we give them a very easy take-home message, and that is that if the relative angular position Ð the o'clock position, if you will Ð doesn't change, regardless of what direction they're going in or you're going in, you're going to have a collision. If they're not moving in your field of view, then you're going to have a collision. And real life examples can make some things easier to understand. Rotational motion and angular stuff is actually some of the hardest stuff we do in intro physics. People don't have a very good intuitive feeling for it, and it causes lots of panic and fear. But when you can show what happens to people who were in a head-on collision vs an off-center collision where a lot of the energy goes into rotation and you have less energy absorbed in the collisionÉNot much of a take-home message, but Ñ if you have that last ounce of control and you're heading toward something, try to move it off center.

"One of the problems I face," explains Professor Syphers, "is that the records [of what happened in the collision] have the problem of perspective, and I can't easily get up in the air to look down on the scene to get a view of what it looks like. I can either make a series of measurements of the tracks if I am there relatively soon after the accident, or I can take the photos and use what I know about optics to correct for the perspective of the camera. This a hand-drawn picture of the scene as it would look from above after I correct for the perspective of the camera."

SH: Do you find in the classroom that maybe some students actually perk up when you talk about this kind of stuff?

DS: Some do, and from some I get the same kind of looks that I get from my children when I try to tell them that sort of thing.

SH: How old are your kids?

DS: 13, 16, and 19.

SH: So the 16 and 19 year-olds have had driving lessons?

DS: Yes, they have.

SH: They must love that! It's not just your standard driving lesson, it's "and now we're going to talk about the physics!"

DS: Which usually gets a response like "Dad, don'tÉ.just don't." Teaching anyone you're related to to drive is already dicey! The human element comes in. The human element comes into the courtroom, into lots of stuff. I've had jurists who've said "yeah, we believe youÉ you're right, he was speeding, but I drive that every day and I always go 15 miles an hour over, and there's no way I'm sending this guy up for what everybody else does.

AB: You must be fun to go to an action movie with.

DS: I have gag orders on me. My wife will not let me open my mouth in movies. The first time I do, she says "IÕm warning now, don"t do that again."

SH: This is why he can play basketball Ð he knows the angles and bounces and all that stuff. Was it you a few years ago who was talking about how many times it was possible for a basketball to bounce on the rim before it would have to fall?

DS: Yeah. There's a limit. Quantum mechanics puts a limit, and it's not hundreds Ð it's something like 13, the number of times a basketball can bounce on the rim and not violate quantum mechanics.

SH: And we all looked at him like "what are you talking about? Give somebody the ball, or we'll bounce you off the rim!"